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Why are light aircraft engines so noisy?
I live near an airport where students spend a lot of time flying circuits. During the base leg, pilots can be heard reducing engine revs prior to the final left/right turn to line up with the runway.
I've often wondered why in this day and age light aircraft engines are not made quieter; the technology seems to be stuck in the 1960's.
Can engines be made quieter or is it so prohibitively expensive/bureaucratic to get an engine through certification that aircraft builders just use off the shelf engines?
What's the quietest light pilot trainer out there (and don't say glider, thank you!)?

I think you may have some misconceptions about where the noise comes from.  To quote wikipedia "Much of the noise of a propeller aircraft is of aerodynamic origin due to the flow of air around the blades." (https://en.wikipedia.org/wiki/Aircraft_noise#Mechanisms_of_sound_production).  They do try to build propellors that are quiet, but that's not really very easily accomplished...  I mean, you can't just put a muffler on a propellor, ya know?

To be honest, GA didn't evolved so much since the 60s, especially compared to commercial aviation.

Yes, GA is largely stuck with 60's technology. Despite a somewhat similar design, for the last couple of decades the average car engine has been more advanced than the average light aircraft one (with some exceptions)

More like its stuck in the 40s.

Propellers are extremely noisy and every little bit of sound you hear from them is an inefficiency.

@Antzi It depends on the size of the craft, I think.  The LSA sector has a bunch of interesting, and actually evolving designs.  But, then again, they have less restrictions viz a vi certification (and, of course are smaller and simpler to design to begin with.)

@IanT8:  I sincerely hope you are not one of the stereotyped people who buys a home near a training airport, then complains about all the noise from student pilots.

Why does it seem that way?  Because it is!

Engines could be made quieter by the simple solution of adding a muffler (or silencer as it's called in some places). They are available for many models and can be installed, at an astronomical cost. The parts and labor are actually pretty cheap, it's the certification costs that make it sting so badly. It costs a lot of money to develop and certify parts for airplanes. Mufflers aren't mandatory, and because they are so expensive to install most don't because the costs so outweigh the benefits - it costs far less to buy a decent active noise reduction headset instead.
Propellers are a big source of noise, and there are quieter designs for many aircraft, however they have to be certified with a particular engine and model of airplane and those costs add up.
The current certification rules are there to keep things safe, in some cases they can stifle innovation. It's why we still have carbureted engines with manual mixture controls instead of computerized fuel injection and turbonormalization.
As for what the quietest trainer is I don't think there's a definitive answer as I don't know of a source of light airplane noise measurements, and any airplane can be used as a trainer. Of the certified light airplanes out there that are commonly used for primary training the Diamond DA20 Katana is the quietest I can think of, that's because it is much lighter than the more common Cessnas and Pipers and therefore uses a smaller engine and propeller. Smaller engine and propeller generally means less noise. Turbo-diesel powered airplanes like the Diamond DA-40s are quieter because the turbo muffles the exhaust noise.

I am not familiar with every small aircraft, but the Cessna, Piper, Beech, and Cirrus planes that I have worked on all have mufflers. Granted they are not very big, but they are there. Check out the Aircraft Spruce catalog for examples. https://www.aircraftspruce.com/search/search.php?s=muffler

Prop powered general aviation aircraft are far louder than automobiles. No pilot flies without a headset because the noise makes it otherwise impossible to communicate with the ground or other pilots. Peak levels exceed 100db and the continuous average is around 85db, which is damaging to hearing without protection. The above charts showing arrival and departure noise are for jet powered aircraft, not the light aircraft in the OP's question.
There are two sources of external noise, the prop and the engine exhaust.
Noise from the prop is caused by its tips approaching supersonic speed. Energy used to produce noise is wasted, so you'd think reducing speed would be helpful. Unfortunately, most piston powered aircraft have props fixed directly to their crankshafts for simplicity and reliability. These engines are already turning slowly (compared to car engines) when producing full power, so slowing them even more drops combustion efficiency faster than it is recovered by increased propulsive efficiency due to reduced noise.
Exhaust noise is caused in aircraft the same way it is in autos. However, the typical aircraft engine used in the trainers mentioned by the OP is a four cylinder turning more slowly, so the combustion events required to make high power are two or three times bigger. Your typical econobox car has a 2 liter motor while the aircraft motor here is almost 6 liters. Exhaust noise is consequently two to three times louder, unmuffled, and more difficult to silence because of the lower frequencies produced by the slow engine. Weight is expensive in an aircraft. Mufflers are heavy and reduce power from the even heavier engine, so the minimum acceptable solution is the one used.
The best way to reduce engine noise is to use an electric motor that has no combustion impulses to suppress. The Pipistrel Alpha Electro is a trainer that does just that. The prop is also sized such that the tips stay between mach 0.5-0.6 during operation, keeping prop noise low. At only 60db, it is far quieter than piston powered aircraft.

Alpha Electro
Gearing a prop to allow it to turn slower and better mufflers could substantially reduce noise. These would both be heavy and raise cost not just for acquisition, but also in use as that weight has to be carried everywhere the aircraft goes. The pilot would still need to have hearing protection due to wind noise in the cockpit, which is not addressed as it was not part of the OP's question.

Edited for clarification due to the useful comments below

In general most light airplanes aren't dramatically louder than most cars (see Estimated Airplane Noise Circular on page say, 140 and Car Interior Noises ). What makes a difference though is how humans perceive these noises. If for example a person stands next to an airplane engine and a car engine at the same sound level we'll see that the main problem with the airplane's engine is that most of the time it emits "annoying" noises that cause discomfort. So it is important not to confuse annoying noises with high dBs! Another point to consider is that during approach -as is the OP's case- the noise from the airplane has less obstacles than when the airplane is on the ground resulting in most cases in lower sound attenuation and higher sound levels received.
Can these piston engines become quieter? Sure they can and a muffler is one thing that would help.
Quite many small airplanes don't have mufflers in order to save on costs, space, engine performance, weight and additional maintenance.
But equally, quite many small airplanes have mufflers for additional reasons related to the exhaust temperatures and yet emit excessive amounts of noise. Why? because engine is not the only noise source on the plane.
However from a manufacturer's point of view one should ask if it is necessary to increase design and operational costs to this end. Once the plane takes off there's no real need for it anyway. And if we take it one step further and consider the regulations we see that since the noises are within the acceptable margins there is no real need to enforce suppression and thus manufacturers don't need to add this additional cost and design changes to their planes.

Furthermore airplanes have additional noise sources resulting from their interaction with the air as you can see in the ICAO's diagram below:

While this is all valid information, it doesn't answer the question of why small GA aircraft are loud.

@FreeMan It does. It gives the reasoning behind the noisy engines and especially answers this part of the question: "I've often wondered why in this day and age light aircraft engines are not made quieter;" Thus as long as the noise level is acceptable there is no need to invest more tech on it or to enforce its suppression.

The majority of your answer centers around the fact that noises are within regulatory limits. You briefly mention at the end that the engine is not the only source of noise. You do not address the OP question of why GA engines are so noisy, especially in comparison to a modern road car engine. Seems I'm not the only one who feels that way. You do, obviously, or you wouldn't have posted your answer.

@ilias you should modify your answer to explicit this information. I suggest you begin your answer with it

@FreeMan I'll modify my answer. However, to be fair, I don't see how the other answer addresses directly the "Why" by merely assuming that all the light airplanes in the OP's area don't have mufflers installed.

I thought the OP asked if small GA aircraft can be made quieter, and if this would be expensive.  I don't see that answer to that question here.

I think the links you provided comparing planes and cars is apples to oranges. The aircraft noise consideration is outside the aircraft at some distance, not the interior noise. I'm trying to imagine what my neighbors would do if I warmed up a C172 in my driveway

@TomMcW apples to oranges? Well not really, if the dBAs are equal then it's still the same sound level received from the ear. Just like equal masses of oranges and apples weigh the same. Car sound levels were added b/c it was requested in the comments, but as I see here p.13, c172 emits 61dBA which is quite common in the car data above and here. Your neighbours will be annoyed of course. It's good not to confuse sound intensity with annoying sounds though.

You're comparing car interior sound levels with exterior levels for aircraft. And the exterior levels are at a given "flyover" distance. What that distance is I don't know, but I'm sure it's defined somewhere in the FAR's. I'm quite sure a C172 is putting out a little bit more than 61 dBA at the 20 feet between my driveway and my neighbor's house. I'm also sure it is more than 61 dBA in the cockpit, otherwise you would not need noise-canceling headphones to talk to the guy next to you

@TomMcW First of all interior/exterior/midair/underground/underwater when the measurements show the same values then they are equal. The car values are there just to give a sense to the reader; and yes the airplane noises are measured at some distance and yes your driveway plane warming would be loud because up close or in the cockpit it emits louder sounds and not the 61dBA measured when approaching by some receiver at distance -not clear above, I'll admit- but still the airplane approach values (exterior) and the car interior noises if they show the same values then they are the same.

The ICAO diagrams here are for jet-powered aircraft. I suspect the distributions are quite different for aircraft with props powered by pistons.


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How fast can an airliner (like a Boeing 747) taxi backwards?
Forgive my lack of understanding, I thought I'd just buy a simulator and mess with it.  I really don't know much of anything in terms of MSFS2020 or simming really at all.
I realize that airliners can taxi backwards.  So, I'm wondering.  At its top speed, how fast can a 747 taxi backwards, if it tried to do so?

Related: https://aviation.stackexchange.com/q/13350/36893

Are you referring to powerback (going backwards using reverse thrust) or pushback (pushed by a tug)?

Have you tried it on the Simulator? Let us know the results.

From a pure theoretical standpoint, the speed limit would be whatever rolling speed can be achieved with max reverse thrust. If you deployed max reverse on a landing, and left the max reverse on until you stopped, then released the brakes and left it on as you started to roll backward, you would accelerate backwards, and if you were able to maintain steering control (unlikely) and the engines were able to operate with the turbulent reverse inlet conditions without stall/surge, you'd accelerate until there was no longer any surplus reverse thrust.
You'd eventually be careening along backwards along the runway at, maybe 30kt, 50kt, 80kt... who knows? You could probably estimate some number based on available thrust and rolling friction/air resistance, but safe to say it's never been tried, or even thought of.  Don't even think of touching the brakes once rolling backward with any velocity.
From a practical standpoint, some operators may allow backing up under reverse thrust in specific circumstances, keeping in mind that you can't see where you're going so people need to be outside to clear the area behind, debris is being stirred up and ingested into the engines (ramp areas are a rich source of luggage zipper tags), and there's the problem of stopping without tipping over onto the tail when braking (the airplane's loaded C of G is not that far ahead of main gear, so it won't take much braking force for inertia to lever it over; safer to use forward thrust to stop than brakes).
So you may see power-back operations in the right circumstances, but the maximum speed in such cases won't generally be faster than a walking, (or maybe jogging) pace.

"Don't even think of touching the brakes once rolling backward with any velocity." Intrigued, why not?

The plane would tip over and hit it's tail on the ground. The center of gravity of planes is just a bit forward (pls note the scientific accuracy here :) of the main landing gear. So even very light braking might end up in a tailstrike.

Added a bit to para 2 to make it clearer.  The other problem is the brakes on a transport a/c are tough to modulate and feel a bit like the air brakes on a transport truck; there's no hydraulic resistance feedback like with car brakes or even light aircraft brakes, you push against springs and the amount of braking is how far you push, with the feedback just being the resistance of springs.

"You'd eventually be careening along backwards along the runway at, maybe 30kt, 50kt, 80kt... who knows?"  - that is the essence of the question, isn't it? I don't see an answer here at the moment.

If you think someone is going to provide a hard and fast number, like 62 kts, you'll need to visit another planet because you aren't going to find that number here.  The answer is, theoretically, indefinite, and in practical terms, a few kts.  We could just close the question as unanswerable, but better to provide some context at least no?

Obviously it's not theoretically infinite, any more than the normal max speed is infinite. You're certainly right that it has never actually been tried, but very certainly wrong that it has never been thought of, and that somebody has run some CFD simulations is also not unlikely. So, no, the question is not unanswerable, though it may be hard to get at the answer.

I said " maybe 30kt, 50kt, 80 kt..., who knows"... INDEFINITE not infinite.  I can tell you that if I walked up to the performance engineering group at the OEM I worked for and asked how fast can I go rolling backwards in a jet, I'd get laughed out of the room. As I said, you could probably estimate some number based on thrust, rolling friction and air resistance, but even if you were able to get it, it would be a guess that would have to be proven by a test, and good luck with that.

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Why would the front edge of an aileron fold outward?
I was just enjoying a movie of one Svetlana Kapanina flying her EA300. One camera looks out of the cockpit over the left wing. In a couple of scenes, the aileron of the wing can be seen quite clearly. The picture (see 1) shows it deflected downward, except for the red "end" deflecting upward. Other scenes show that when the aileron deflects upward, the red "end" turns downwards.
What is the reason to have this red "end" tilting in opposite direction to the aileron?

NB, you can enjoy the whole movie here:

That is an enclosure for a counterweight, either made from steel or lead to balance the aileron and/or reduce control flutter in various flight regimes. The extension provides an additional lever arm to alter the moment of inertia about the aileron’s axis of rotation.  These are usually added or refined during flight testing to remove undesirable flutter or other qualities inherent in the design.  Counterweights are usually installed at the factory with the airplane but custom made counterweights can be used on a specific aircraft to provide a specific feel to the controls to meet customer requirements.  Many high performance experimental category acro aircraft do this on aircraft custom built for a master aerobatic flyer.
The comment above about this providing an aerodynamic counterbalance is incorrect.  Such devices for this purpose do exist but in the form or one or more ‘shovels’ or ‘spades’ on the underside of the control surface.

If you would like to add a source: POH Section 7.3

@qq jkztd: the POH says "To reduce pilot's hand forces the hinge line of the ailerons is positioned 25% of the aileron depth." In other words, the entire aileron is aerodynamically balanced to reduce control forces.

The small red tab is an aerodynamic balance, used the reduce the control loads required from the pilot when power assistance is not available.
Normally, the aerodynamic load on a deflected aileron will tend to return it to a neutral position. For slow and light aircraft the pilot can easily handle the required load to maintain the required deflection. For high performance aircraft these loads can be come significant.
By adding a small part of the aileron ahed of the pivot (a horn), the aerodynamic load on that portion will tend to deflect the aileron further into the flow. The tab is still small enough that the main part of the aileron will return the surface to neutral, but the force from the horn effectively lightens the load that the pilot needs to handle.
The EA300 is a high performance aerobatic aircraft. The pilot needs light control loads in order to perform the extreme maneuvres the aircraft is capable of. Using aerodynamic balances achieves that without the need for a heavy hydraulic system.
You may also find aerodynamic balances on the elevators and rudder of some aircraft, for the same reason.
The geometric shape trailing from the wing is a sighting aid to help the pilot judge the aircraft attitude with respect to the horizon - nothing to do with the ailerons at all.

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What should be my basis for selecting an airfoil?
We're in the process of designing a trainer aircraft and I wanted a high wing aircraft. We calculated this from the profile graphs given on the reports.I know these aren't super accurate since I just projected the values from the graphs.
Don't  mind the highlights

For trainer aircraft, the major design driver in wing profile selection is stalling behaviour. Ample warning, docile & progressive stall, no sudden surprises. Stall behaviour must be demonstrated during certification. From Torenbeek:

The stall should preferably be characterized by a distinct and initially uncontrollable nose-down pitching motion, and during recovery to level flight it must be possible to prevent angles of roll and yaw of more than approximately 15 degrees (light aircraft)..

The NACA 4- and 5-series have been around for a while and there has been much experience with the application of them. Again from Torenbeek, fig 7-12:

Four-digit

The NACA four-digit wing sections ... are by no means low-drag profiles, (but)
  the drag increase with lift is fairly gradual. The cambered sections have rel- atively high maximum lift and the stalling is fairly docile.
In view of the gradual changes in drag and pitching moment with 11ft, the 4-digit sections are frequently used for light trainers, which often fly in different conditions.

Five-digit

The NACA 5-digit wing sections ... have the highest maximum lift of the standard NACA sections, but the stalling behavior is not particularly favorable and rather sensitive to scale effects.

This can be seen in the $C_l$-$\alpha$ curve B above, which drops off suddenly and dramatically after max $C_l$
NASA report CR-1646 has more information on the stalling behaviour of NACA profiles.

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How is the cruise speed of an aircraft chosen?
Does cruising speed of aircraft depend upon mass of aircraft?
I am asking this because as lift is generated to overcome the gravitational forces ($mg$). And lift is proportional to square of the aircraft velocity.

and the area of the wing

The speed of the aircraft in cruise is determined by the forces in the horizontal axis: thrust and drag. Weight and lift are forces in the vertical axis; they do pop up in the horizontal axis, but are relatively tiny in cruise.
Image source
At low airspeeds, induced drag is the dominant factor: this is the drag that is proportional to lift and weight. At cruise speeds, induced drag drops off and parasite drag rises quadratically with airspeed. It is drag associated with the aerodynamic shape of the aircraft. At any weight, the most beneficial shape is the one that aligns the fuselage best with the free air stream: tilt the nose up or down from the Angle of Attack for minimum parasite drag and drag will increase, at any speed and weight. Wind tunnel tests and Computed Fluid Dynamics are the tools used for establishing minimal form drag.
However, for straight and level flight the vertical component of lift must indeed match the weight, so one of the parameters of the flight state must be tuned in order to get zero climb rate. Changing cruise speed is indeed one of the degrees of freedom to change lift, but not the best one. In the aircraft aerodynamic axes, lift L is given as $$L = C_L \cdot \frac{1}{2} \cdot \rho \cdot V^2 \cdot S$$
S is wing area, usually a constant that cannot be changed during cruise. So the degrees of freedom to change lift are:

Change lift coefficient $C_L$: this is done by changing Angle of Attack, by pitching up or down. Doing so creates extra drag and fuel burn, the least amount of drag is generally with the fuselage aligned with the free stream.
Change air density $\rho$: fly higher or lower. This is what is done when the aircraft gets lighter due to fuel burned: at higher altitude there is less air resistance and less thrust needs to be delivered by the engine, improving fuel burn without slowing down.
Change V. Flying slower as fuel is burned is beneficial for fuel burn per hour - but it takes longer for the aircraft to arrive, so fuel is burned for more hours.

So for varying weight, it is best to vary lift by varying altitude. Long range cruise aircraft would have the least fuel burn if they could gradually climb as fuel weight diminishes, however there are air traffic corridors which the aircraft needs to stay in. Cruise climb is done in steps instead.

From this lecture, which also provides equations for cruising at constant altitude (varying velocity) and at constant velocity (varying altitude). The latter wins.

Wing area is usually constant. *8')

I think there should be a caveat that this is a significant simplification and that the true way of determining such things is of course finite element analysis, etc as well as wind tunnel tests. Nobody really uses that formula in practice.

@Koyovis I hope it didn’t come across as a negative comment. To clarify I think there should just be a caveat to the reader to take it with a pinch of salt, so to speak.

@user1997744 Plz check page 24 of the linked Princeton lecture, where they use the equation.

@user1997744 I work extensively with operational aircraft performance, and I don’t believe I have ever seen something like finite element analysis used outside of university or maybe at the aircraft manufacturer. As an aircraft operator, the above formula is normally good enough - most of the time, you‘d use tabulated data from the manufacturer with linear interpolation in between data points! It’s an incredibly inaccurate science in real life, anyway.

@CptReynolds Oh, absolutely, I wouldn't expect an aircraft operator to do that. What I meant was the manufacturer would be using such methods to determine suitable cruising speeds.

@user1997744 Makes sense! I understood the question to be geared towards operations, hence my comment. At the manufacturer, design methods come into play which are much more accurate and include wind tunnel tests and computational fluid dynamics.

@user1997744 I understand the meaning of your original comment better now and have expanded the answer.

The most efficient cruise speed of a given aircraft depends, among other parameters, on the aircraft‘s mass in the way you hint at. The operationally flown cruise speed may differ and may thus be, within a certain speed range, selected independently of mass, e.g. for air traffic control reasons. That safe speed range, however, again depends on mass (among other parameters).

It means heavily loaded aircraft reach to it's destination earlier as compared with less loaded aircraft..?

You wrote "The operationally flown cruise speed may differ and may thus be, within a certain speed range, selected independently of mass" I didn't understand that part :)

@AbhishekAcharya Yes, if the same aircraft is loaded heavier, its best cruise speed will be higher than if it is lighter, all else being equal. What I meant with the other sentence is that there is a mass-dependent minimum speed (heavier mass, higher speed) and a fix maximum speed for any aircraft, and the cruise speed must be between the two.

if aircraft is cruising with a speed which is not equal to best cruising speed than what does pilot do to balance lift .. ?

@AbhishekAcharya I am not sure I understand the question. Lift force is dependent on the air density, the airspeed, the angle of attack (angle between direction of travel through air and longitudinal aircraft axis) and aircraft geometry including the wing surface. Assuming fixed geometry and air density, the aircraft can still be operated at different speeds, as long as the associated angle of attack can be flown. Simply speaking, the slower the aircraft flies, the higher the nose (even in level flight). Did that help?

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RWY designation
I'm a translator, and currently I have some issues associated with RWY designation.
There is a runway with the magnetic direction 246°. How would you call it?
So let me put it like this. In Wikipedia, they say that you truncate the three-digits magnetic direction to the first two figures and you get 24, while in some other places it is said to round the result up or down, so I shall get 25.
Which is correct? Will it be RWY24 or RW25?

Everything i've seen indicates rounding rather than truncating, though I /haven't/ seen any mentions if headings ending in 5 use round-to-even or something else.  …  Also, is this a real airport? You should just be able to find the published approach docs or similar if so. Heck a satellite map might verify the numbers physically (if the magnetic state of the area hasn't changed lately…)

@Pete what do you mean? There are many airports with parallel runways. Atlanta Hartsfield has even 5 runways in exactly the same direction. Approaching from the west they are named 8L, 8R, 9L 9R and 10 from north to south. So sometimes truncating, rounding & being creative is being used.


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Are there typical values of pitot-static and TAT probe measurement uncertainties?
I'm working on flight sensors for a project and I'm supposed to model noise in the Static Port, Pitot tube, and TAT probe measurements. I looked a lot for it online and could not get a convincing answer.
I need the uncertainties of Static port, Pitot tubes and TAT measurements. By uncertainty, I mean + or - certain pascals for Static port and Pitot tubes and + or - certain degree Kelvin for the TAT probe. Is there a typical uncertainty value for these, say for example a Boeing 747 and I guess a digital sensor as the worse case? I don't know much about the companies supplying these sensors or the installation method on the aircraft.
It would be great if someone could help me! Cheers!

This question is really too broad, as the answer would be affected by all sorts of factors: Which aircraft, which pitot tube/static port, the actual installation of the aircraft. Are you using an analog or digital sensor. Digital sensors would have their own noise you would need to filter out.

I have modified the question to make it easier. Thank you!

I'm also confused as to what the purpose is of modelling "noise" when you don't have a defined sensor, pitot tube, static port, or outside air temp probe. Each one is going to be different.

It is for demonstrating noise effects in an ADIRU algorithm. All I need is a typical value of uncertainty in each of these sensors for a wide body jet, as I couldn't find those. My noise model is ready and I all I need to finish them are these uncertainty values.

The pressure and temperature measurement devices are analog instruments, extracting parameters that are of value to pilots from physical phenomena. Unfortunately, the physical world throws in a variety of effects, linear and non-linear, that make it difficult to extract the parameter of value. Noise is one of them, but in a way that is exactly what we want to measure since pressure is just the average value of noise in the speed of gas molecules in air.
In the pitot tube there are a couple of effects that make the measurements non-trivial:

Friction between the air and the tube causes a velocity distribution that varies with flow radius relative to tube radius.
Fluid mechanics causes different behaviour at different conditions, such as laminar or turbulent flow, or supersonic shock waves.
Inertia of the particles creates a time delay in pressure measurements as a function of airspeed and could can cause back pressure surges.
Old fashioned thermodynamics such as the ideal gas law impose non-linear functions on the relationship between pressure, volume and temperature.

From Wiki
All these effects need to be considered in order to measure just the total pressure and the static pressure, and then to extract the airspeed, altitude etc from these.
If it is calibration data of the sensors that you are after, that science is fortunately over 100 years old.

I'm sorry, maybe the word model was confusing. I know the modelling part in a way but I'm stuck as I need some typical/realistic values of measurement uncertainties for these three.


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Can this design provide more lift force than thrust from engine?
The problem is depicted in the picture:

Generally, why we don't use engine blow wings to fly? Can we use wind-tunnel-like wing to generate lift force?
Can it generate more lift than thrust? If it can, how many times?

Possible duplicate of Could a blown wing ever be powerful enough to lift an aircraft at zero forward velocity?

The question, while similar, includes the added twist of using multiple wings...I tried to focus on that in my question.  The question you reference is probably a good follow up to finish it off.

@PeterSchilling that is how I read the question also. But upon re-reading it, it doesn't saying anything about lifting off at zero forward velocity. If aircraft weighs 1000, fan thrust is 200, and lift is 201, then answer is yes, it produces more lift force than engine thrust, however no lift off.  The first sentence in Marius' answer below answers the question. No free lunch.

@PeterSchilling I have to agree with Devil, this isn't a dupe, since that question asked specifically about taking off with zero forward velocity (which, incidentally, was fun to answer.)

@Marius, while this question might be adding a twist with multiple wings, it changes absolutely nothing on the conservation argument that trivially prevents it whether there is one wing or more.

Because there is no free lunch.  A single wing behind a propeller or a fan can see some amount of performance gain from being in the propeller's slipstream, but, when you start stacking multiple wings together...it gets a little trickier.
A single wing can get an advantage from the swirl induced by the propeller, in addition to the increased speed you've remarked upon.  In a thesis written by LLM Veldhuis on wing propeller interactions, he notes that, when you have a propeller operating in front of a wing and rotating such that the inboard blade is always moving up, it changes the local angle of attack on the wing behind the propeller.  This modifies the lift distribution (notionally shown in the figure below) and ultimately decreases the induced drag of the wing for a given operating lift coefficient.  A set of experiments by Witkowski et. al. (Propeller/wing interaction) in the 1980s recorded a wing seeing up to 40% savings in induced drag based on the adjustment of a tractor propeller's rotation rate!

This is what I've, at least, seen cited at the most prominent effect of having a tractor propeller in front to of a wing.  If you have a small enough wing, though, say on the scale of UAV, there's a good chance you could have a significant portion of your wing in the propwash, which can keep the flow attached to the wing at higher angles of attack, letting you, potentially, keep a control surface or two unstalled and able to maneuver the aircraft when they normally wouldn't.
However, that's not lift, and it doesn't quite answer the question about the multiplane setup.  The problem with stacking wings so closely to each other goes back to investigations in the 1920s and can be most easily explained, I think, with the venturi effect.  When air is accelerated by the curvature of a wing, the static pressure decreases and you can a suction force, which, on the upper surface of a wing, translates into lift.  However, stack two wings (or other objects) closer together (as in the picture below), and you get something...not so good.  The image below is from a conceptual rotorcraft design submitted by the University of Maryland for the 2016 American Helicopter Society Graduate Design Contest and is a kinda strange thing called a quadrotor-biplane-tailsitter (we named it Halcyon).  However, the upshot of the image (which is colored by local pressure -- the more negative the Cp, the lower the pressure) is that, due to the wings and fuselage (the bit in the middle), you are playing a game of diminishing returns.

While the bottom wing sees very high velocity air going over it, leading to very high lift, that same low pressure zone also generates a strong downforce on the fuselage, effectively mitigating a lot of your lift (the design team estimated that it killed almost all of it, actually) from the lower wing.  The upper wing, since there's a little extra space, isn't as effected by that same phenomenon, so, in the end, the aircraft had enough lift, in theory, to fly...but it's not an efficient configuration at all.  The same would be true for a stack of wings.  In a 1923 paper by Max Munk entitled General Biplane Theory, he estimates that, in order to minimize interference effects between wings, they should be spaced apart by at least 3 chord lengths.  That would easily move your wings so far apart that not even two wings could easily stay in the propeller wake...at least for full size aircraft.

I am gonna read all papers and designs you referred, and reply later

Fist, I find it odd that your fan lists its thrust in the unit of a mass. Thrust should be a force, not a mass. Now let's assume that this means the thrust is equivalent to the weight force of this mass in the gravitational field of earth (g = 9.80665 m/s²) and we get the actual thrust of 11.768 N.
Thrust is the mass flow times the speed difference between intake and exit flow. In the static case and using the Froude hypothesis, this means: $$v_{exit} = 2\cdot \sqrt{\frac{8\cdot T}{\pi\cdot d^2_{Fan}\cdot\rho}} = 141.3\:m/s$$
Unfortunately, jet contraction means that only a small part of the wing behind the fan will experience this airspeed. Generally, lift is created by a wing by deflecting the air downwards. Normally, a big mass of air is deflected by a small amount, because this results in the best efficiency. If you insist on using a smaller wing and a higher deflection angle, efficiency will suffer. The number of wings will not affect the result - a single wing will create as much lift as any stack of multiple wings, only with less friction drag.
Why is that? Lift is caused by deflecting air, and this deflecting is done by a pressure field that needs suction on the top surface of the wing and overpressure on the bottom surface. In a stack of wings, the suction of the lower wing will also act on the bottom of the upper wing, so in effect only the suction on the topmost wing and the pressure below the bottommost wing will add a net amount of lift. It's better to reduce that stack to a single wing where every surface can contribute lift.
If you want as much lift as thrust is created by the fan, the wing would need to deflect the exit stream completely downward, by 90°. This is far above any realistic value for a wing (or a stack of them). It will be better to place the wing at some distance from the fan exhaust. Then the exhaust stream will suck in air from the sides, so the mass of air being thrown at the wing will increase while its speed will decrease. Now the same lift can be created with less flow deflection, but still the possible lift will be lower than the thrust of the fan.
Next, your airfoil shape sucks for this application. You want maximum deflection and have a fixed angle at which the air hits the wing. Thus, you can afford a small leading edge radius and need a lot more camber. Like the airfoil of a Fowler flap! In order to increase the deflection angle, it will help to add a second flap with a gap between the two. And a third. This has been taken to its extreme by Frederick Handley Page in 1921 when he  modified an RAF 19 airfoil with 7 slots for maximum lift, such that a staggered configuration of 8 airfoils resulted. Note that the airfoils are not at the same streamwise location but each sits below the wake of the preceding airfoil.

Handley-Page 8 element airfoil, taken from this paper by A. M. O. Smith, McDonnell-Douglas)
Now it must be said that deflecting the flow will incur drag. If the flow is turned by 90°, even under ideal conditions will the drag be at least as big as the thrust. If you draw a box around the fan-wing combination and integrate over the edges, you will find that no horizontal component is left in the exiting airstream, so no net thrust is created by this contraption.
Wouldn't it be better to swivel the fan to 90° in order to use its thrust for lift?
If you use the fan thrust to move the fan-wing combination though air, then the wing can work on all the air that is coming at it. Make it big and move fast enough and lift will indeed be larger than thrust. To improve efficiency, replace the fan by a decent propeller and compare the result to the status quo.
In order to maximize the lift potential of the accelerated air stream of a fan (or propeller), blown wing designs showed superior low-speed capabilities as long as the engines were running. One example is the Custer Channel wing as used on the CCW-5 shown below (source).

Another example is the Boeing YC-14 experimental tactical transport aircraft shown below during construction with the blown flaps fully extended (source).

I am gonna read all papers and designs you referred, and reply later

No. The thrust that the engine provides is the thrust that the engine provides, no matter how you wish to tilt the exhaust flow:

Tilt the whole engine and the thrust will be vertical. Make the fan blades much longer and you have a helicopter.
With the engine horizontal, mount a flat plate under 45 deg and the horizontal thrust will be deflected downward, minus not inconsiderable losses due to flat plate drag.
Mount a wing profile and the thrust will be tilted slightly downward, with some losses, much less than above due to the pressure suction peak at the profile nose, providing much lower drag than a flat plate.
Mount two wing profiles in the exhaust stream and you've created a bi-plane. Does the same as the single wing above, but with more losses due to more drag.
Mount many wing profiles and you have more losses due to drag. This configuration was tested and failed.

The lift from the airfoil generates is from behind your CG, so your mass in front pushes the nose down and the tail is raised by the wing, which means your plane will tip forwards (downwards). Also the wing interference thing everyone else’s already mentioned.  Also turbulent air is not very useful for lift and bad for control


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Do UAVs use ground-based navaids?
When I Googled it seems it is not common to use Vortac like systems from UAVs as a backup to GNSS outages, like in manned aircraft. And also I haven't seen any equipment designed for just UAV platforms, it's all designed for in-cockpit use.
Why do UAVs not use ground-based navaids?

There are at least three reasons. First, UAVs don’t fly on airways, so VORs aren’t particularly useful. Second, is size. GPS receivers and antennas are smaller than a pack of gum. A VOR antenna is at least 12 inches long, and you need two branches. Plus the receivers weigh a lot. Third is programmability. GPS receivers contain location, altitude, and speed data in digital form that can be transmitted to the controller or used for autonomous control.

TACAN is a military version of VOR. It also transmits a DME signal that is used by both military and civilian pilots. I don’t know anything about the antenna size and receiver weight but I’d imagine that they are similar to VORs.

@JScarry, a VOR antenna is normally a 1/4 wave horizontally polarized antenna.  In most aircraft each 1/4 wave is mounted on either side of the vertical stabilizer. But with one VOR receiver, one would only need one antenna. The actual VOR electronics can be rather small, but it has not gone through the mass production and miniaturization that GPS has, and the production volumes are low, so it won't get much more enhancement.

@mongo Now that I think about it, I do have a handheld aviation radio that has a VOR receiver and display in it. With the battery it weighs less than a pound (.4 kg) and the antenna is about 6 inches (150 mm) long. So someone probably could make a VOR receiver for UAVs if there was any demand for them.

@JScarry, as indicated in my answer, the service volume, the spatial resolution and the repeatability of VORTACs is inconsistent with the mission of domestic sUAS. I can buy GPS with antenna, USB interface and WAAS, GLONASS, etc. for about $18 in small quantities. The VOR handheld receiver separated out would be much more, and it doesn't come close to meeting the use cases for a GPS in a sUAS. The handheld antenna is likely a wound 1/4 wave, which results in some loss. Do you get a VOR signal on the surface from where you would launch a sUAS? Probably not.

@user107577 VOR service volumes in the US are 20 nm for terminal VORs (used for approaches), 40 nm for low altitude VORs, and for high altitude VORs 40 nm below 14,500' and 100 nm from 14,500' to 18,000'. For most small UAV purposes you would have to be within 40 nm and line of sight to the VOR and unless close to the VOR above 1,000'. https://www.touringmachine.com/Articles/instruments/34/

For UAS, the aircraft may be below the service volume of a VORTAC most of the time.  Furthermore in the US sUAS are normally line of sight to the pilot so in theory if GNSS is unavailable, the pilot will control visually.  Finally the variability and uncertainty of VORTAC is high enough so as to make it impractical for UAS stability, drift and position control


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How is health monitoring of large aircraft engines and components done?
How is online (in-flight) and offline (between flights) health monitoring of large aircraft engines and other essential components done?
As far as I have been told, there are a lot of measured channels (at least for engines), but:

what exactly is measured?
How are the data evaluated during flight?
How are the data evaluated on the ground (from long term point of view or after/before failure)?

EDIT: You can consider Boeing 747 or 787 as a large aircraft (to narrow down the question as requested).

Related: The overall picture of Flight Data Monitoring (FDM). Quick Access Recorder (QAR) and FDM on ATR.

BY wIRELESS SENSING ,INTERNAL AND EXTENAL INSPECTION,CHECKING FOR CRACKS, DISTORTION,BURNIG,FRETTING wEAR AND HOT SPOTS

Asking what is measured is very broad as you're not limiting it to engines - there are so many parameters.

@ATHIRAMOL.M.R Check your Caps-Key.

@user1997744 Fair point probably, I edit my question to make it more concrete.

Methods of recording data and what's monitored differ between manufacturers but speaking as a Rolls Royce employee, the engine I'm responsible for, the AE2100D3 on the Hercules, is done via downloads. The flight computer records many different channels during flights and ground runs which are downloaded daily, then trended and analyzed. RR HQ then flag any anomalys and send out data for customers to act on, i.e. vibration problems, reduced performance etc. Big engine such as Trents are monitored in real time whilst they fly which is really impressive.

As regards to what exactly is measured, I could list lots of stuff but primarily it's broken down into vibration (all rotating components vibrate, and have allowable limits for this) and performance (referencing pressures and temperatures through the engine to give a performance margin or figure) Anything that either exceeds or drops below set limits raises a maintenance alert.
Engine control units/FADECs constantly monitor all sensors, as do the crews, again anything that needs attention will trigger some sort of warning or information system
Generally through trending and graphs, or in terms of component lifing, etc there will be a count.


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How does an airline develop a Safety Management System (SMS) program?
How does an airline develop an SMS program? Like from the ground up. And who does it involve? Does it involve regulators?
I know the 4 pillars but who does it involve?

I would start by hiring someone who has one it before.

How large is your operation ?

@skipper44 just a typical legacy carrier.

Start with AC120-92

A good first step is to have your CEO downwards attend an official SMS workshop or class. Not only is it a requirement for implementation, but it gives the necessary orientation for the top brass to understand the system and hence their responsibility and commitment as 'Accountable Manager' etc.
When SMS was first introduced well over a decade ago, ICAO had provided for a phased implementation for States and Operators over a 3(?) year period. Even the best run organisations were 'novices' when it came to this task. More recent documentation showed an 18 month implementation, and the latest documents seem not to provide a timeline. This is probably due to the fact that there is now a huge amount of experience gained worldwide by both regulator and industry. Here's a useful intro video provided by the UK CAA:

The process of setting up SMS for an Airline should ideally have a Safety Manager exclusively attached to the task through the 3 implementation phases. And YES, the Regulator is intimately involved in the process of implementation and after.
Here's some FAQ answered by the UK CAA and below that some FAA guidance on the implementation of the 3 'Levels.

In case your's is a smaller operation, there's guidance available with most regulators to address the implementation appropriately.
In any case, do check for the latest rules with your regulator.


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In the USA, how much more expensive is 100LL compared to Jet-A1?
I have never flown an aircraft before and do not have any clue of what the fuel prices are. I was doing some research recently and found that some websites say Jet-A1 costs about 1.5 - 2 dollars per gallon while many others say it is about 4.3 dollars. However, all websites put the cost of 100LL avgas at around 5.1 dollars. I assume the 4.3 figure includes the additional charge of refuelling at the airport but I haven't found anything that mentions this (if it's true). But do airlines pay this price or do they refuel their planes by themselves and purchase the fuel wholesale at $1.5 dollars per gallon thereby minimising refuelling cost? And if so, can general aviation aircraft do the same - buy the 100LL fuel at wholesale for a cheaper price and fuel their own planes?
In practice, what is the difference between the price that airlines pay for Jet-A1 and what general aviation pilots are paying?

Prices vary widely around the world, you need to focus this down to an area or ask something specific.

I was referring to the national averages in the U.S.

Skyvector has current prices of both in USA. Open the Layers toolbox and under the FBOs tab select which ones you want to see.

The prices vary widely in the US depending on where you are and the type of airport you are at. Major class B airports and class D satellite airports in big cities tend to have the highest prices I have ever seen when flying. Most prices are listed publicly if you would like to look up anything specific but this study has some decent summary data for airports they included that may interest you:

As for why the price is different, its mostly a supply and demand issue. The country (and for that matter the globe) simply uses a lot less 100L than it does Jet A.
If you have a place to store 100LL you sure can buy it in bulk but most guys putting around in a 172 don't have that kind of luxury.

This is surprising. I thought Jet A was substantially cheaper, not a little bit cheaper.

Do these numbers include taxes? At least here in Germany, the fuel is taxed differently for private vs. commercial use, which makes up most of the difference, IIRC.

@JohnK One can negotiate substantially lower prices when buying in bulk, and jets (and especially airlines) use a lot more fuel than pistons. That leads to a much greater difference in actual prices paid than retail pricing would indicate.

The Airnav site you linked to is a very good source for fuel costs.  I've used it extensively when planning flights.  I'll usually top off my tanks at whatever FBO has cheaper fuel when I'm flying around the local areas since the airport that I'm based at is most definitely NOT one of the cheaper ones.

Then there's the 65 cents/gal difference between the major airport  and the mostly GA airport 20 miles south.  And at that airport, there's a 1.14 dollar/gal difference between the FBO coming out to your plane with a fuel truck, and you taxiing up to the self-serve pump: https://www.airnav.com/airport/KCXP/MOUNTAIN_WEST

@StephenS  They also purchase futures contracts for their bulk fuel to provide more stability for planning purposes.

As you said, the national average for Jet-A1 is listed at around 4.8 dollars. So why do some websites list its price around 1.5 dollars? Is it because of airline negotiations or just incorrect? - https://www.airlines.org/argus-us-jet-fuel-index/ - https://www.iata.org/en/publications/economics/fuel-monitor/ (I think this one is international though)


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Any ideas on what this aircraft is? The number 5964 is printed in the negative

Any ideas on what this aircraft is? The number 5964 is printed in the negative

Welcome to Aviation.SE! If you have any additional information (e.g. when and where the photograph was taken), please add them to the question.

Looks like a 5962 to me, not a 5964...

It is a 1911 “Uniplan” designed and built by Arthur and Georges Gonnel. It is unlikely it ever flew.
Photo source and addition information

This photo shows the strange contraption conceived by Arthur and Georges Gonnel, an "aerian" teted in March 1911 in Juvisy. The pilot Pappaert did not own an official flying license. He didn't manage to take off and that was the end of it... The "uniplan" had a 3.20 m wingspan, was 7 m long and and 3.33 m high. Wing area was 34 sq. m. It weighed approximately 300 kg when fully loaded. Built around an uncovered twin-boom fuselage directly connected to a kite-type wing by V-shaped tubes, and powered by a 28 hp 2-cylinder Velox-Suère engine, the aircraft was subsequently heavily modified: the photo represents it with a new fuselage and a 50 hp Velox-Suère engine with 4 staggered cylinders.
This strange design by Arthur and Georges Gonnel was completed and tested by Pappaert at Juvisy in March 1911; it is unlikely to have flown. A square-sectioned uncovered fuselage sat on 2 wheels; the engine was set inside just over the wheels and drove a tractor propeller through a shaft. Above the fuselage, extending its whole length and about as wide, was a long covered boxlike frame, with fabric-covered extensions down each side, making rudimentary wings or fins. The underside of the box was left open, in which the air stream was to "induce a lifting reaction which ought to make it fly."
The machine was to be operated from roads: it was named Uniplan.
(Span: 3.2 m; length: 7 m; height: 3.33 m; wing area: 34 sqm; gross weight: c 300 kg; 30 hp Velox Suer)

That's no way that's going to fly!

Always best to include the actual text, not just a screen shot of it. That way, those who use screen readers can have a chance. Plus, it's just easier to read for those whose eyesight isn't as perfect as they might like.

Thanks, I’ll do that next time.

It is fortunate that les frères Gonnell decided to bring the leading edges of the vertical panels together in a kind of boat prow, diverting the airflow away from the box interior and creating an area of low pressure that destroys any hope of actual flight. Otherwise, the thing might have developed enough lift in ground effect to actually rise from the runway, in which case Pappaert certainly would have been killed.

@A.I.Breveleri It should be noted in context that given the aerodynamic knowledge of most aircraft builders of the time, this device would have appeared to the aspiring engineer no more dangerous than any other contraption of the time. That era was an era of experimentation - which in my opinion didn't end until the onset of WWI. Some flew, most didn't, some were killed, and that's how we learned.

@dotancohen The sad thing is that basic aerodynamics and flight stability was fairly well understood (though most still didn't understand adverse yaw) at that time from knowledge developed by Lilienthal etc. but a lot of inventors and engineers kind of ignored the more technical aspects and relied on intuition.

@FreeMan, thank you for not just making that suggestion in the comment, but actually making the effort of transcribing the text yourself. I really appreciate the constructive attitude and the contribution to the community moderation process.


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Do you need a Commercial Pilot Certificate to fly an aircraft you own for aerial survey work?
Is it legal for a Private Pilot to fly his own aircraft (owned by the pilot) to perform aerial surveying/mapping for a company that he owns?  He sells the data to another company that he also owns.

Welcome to Aviation.SE! For questions about legality, please always include which country you are asking about.

This is probably illegal. In the Perry interpretation, the FAA considers a similar situation and decides it is illegal.
In order for aviation to be "incidental" to business, you need to remove aviation from the business and see if that changes the fundamental character of the business. If the data you're selling is something you could collect just as well without an airplane, you might have an argument. Certainly selling any of the actual photos taken is verboten.

That letter highlights how even the FAA can't agree on these questions!

The answer is, it depends.
14 CFR 61.113, Private pilot privileges and limitations: Pilot in command, states:

(b) A private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any business or employment if:
(1) The flight is only incidental to that business or employment; and
(2) The aircraft does not carry passengers or property for compensation or hire..

I tend to favor the most permissive interpretations, and would be inclined to say that you could do this on a Private Certificate, but the legalities would hinge on how your characterize your business.
For example, if your business model is interpreting, processing, packaging and selling a data product, and the raw data could also be gathered by means other than flying, then one could argue that flying is incidental to collecting the raw data.  (saving hours or days of driving - just like flying vs driving to meet a client to sell life insurance is incidental to the act of selling.)
If, however, you market yourself to the public as an on-demand aerial survey company you would put yourself in a very different legal position.  If you have concerns about this you would be wise to consult with an aviation attorney.

How is performing aerial surveying and then selling that data "only incidental to that business"? Sounds more like a major part of the business to me...

Right, gathering and selling survey data is the primary business, and the regs applies to ANY business.  It's the "acting as PIC" that's incidental.  If you were acting as PIC for someone else's survey business and getting paid for it that would be different.

@Bianfable, good point though, thanks. Please see my edits and let me know what you think...


text:
How to fly the step-down fixes on the LOC 32 approach at Dothan (KDHN)?
From Oaldy to CABTA is 2600, then is it CABTA to KENSY down to 2200? Using Localizer only...I see the glideslope intercept says 2200 but Kensy is father up.

What do you mean by "KENSY is farther up"?  Are you looking at the 6K' on the profile view?

If you’re flying the LOC, the GSIP (lightning bolt) is irrelevant.

OALDY to CABTA is at or above 2600
CABTA itself is at or below 6000
CABTA to KENSY is at or above 2200
KENSY is the FAF, and then you can descend to the MDA of 1220
If you can identify FEKRA, you can descend to a new MDA of 720

That approach plate can be a bit confusing at first.
If you fly a straight in LOC approach via IAF OADLY you assumed correctly that you need to be at 2600ft or above until CABTA and then you can descent to 2200ft or above until KENSY. Those published altitudes are considered minimum altitudes.
At KENSY you are going to start your final descent and you'll be a little bit (33ft) above a 3° profile. You can deduct that from 2167ft crossing height at KENSY published for the ILS version for this approach.
I'm not entirely sure what you mean by "Kensy is father up" in your question but I have the suspicion that you got confused by the profile view. Keep in mind that the profile view visualises the procedure turn portion of the approach with KENSY as IAF. These altitudes (up to crossing KENSY again) are not applicable for your straight in approach via OADLY.


text:
How come nobody survived Air Moorea 1121, yet other people have survived crashes from altitudes more than 90x higher?
Air Moorea 1121 crashed from no more than 400 feet, yet people have survived far more awful disasters, such as UA232 or JAL123.

How come people die in car crashes, at zero altitude?  Hint: It's not how high you are that matters, but how fast you're going when you hit.

I'm guessing you consider your examples to be crashes from "90x higher" because the initiating events happened at high altitude. This extra altitude was actually a good thing in these cases, because while the pilots lost most control of the aircraft, they were still left with partial control. The extra altitude gave them plenty of room to figure out what was wrong with the airplane and how to control it with what was still working. This allowed them to end up in more of a crash landing rather than just a crash. In airliners that really do crash from higher altitudes, there are no survivors.
United 232 was more of a crash landing. Although the hydraulic systems were lost, the plane was still trimmed for level flight and the pilots could use the remaining engines to control the plane. They had plenty of altitude and airspeed at the time of the engine failure to get the plane under control and figure this out. This resulted in the crash landing where about 2/3 of the people on board survived.
Japan Air 123 was similar in that the aircraft lost hydraulics but they also lost most of the vertical stabilizer. Again, this happened at a higher altitude which gave the pilots room to react to the issue. The pilots still managed to fly the plane for a while but ended up crashing into the mountains. The survival rate was less than 1% though this was partially due to delay in the rescue operation.
Air Moorea Flight 1121 lost its elevator control cable. While the pilot could have used trim to control the aircraft's pitch, the airplane initially entered a dive and 400 feet was much too low to recover from this. If the cable had broken at a much higher altitude it's possible the pilot could have regained control.
Another point to remember is that in a large airliner like the DC-10, the passengers have a lot around them to cushion the impact. In a small plane like the DHC-6 this isn't the case. A crash into the water also results in a much higher impact, and any survivors would have to be able to swim free to the surface.

Usually no survivors.

From 400 feet or 40000 feet the most important factors in surviving a crash are how fast you are going and how sudden the stop is. In Morea 1121 the elevator cable snapped and the airplane became uncontrollable, pitching down and impacting terrain at high speed, the airplane came to a very sudden stop. In UA232 the airplane was still controllable to a degree, the pilots were able to get the airplane close to the ground and when it crashed the energy was dissipated over a longer period of time. The fuselage of UA232 was able to absorb some of the energy and protect some of the people on board.

Air Moorea 1121 was unsurvivable due to the high G forces of the impact with the water. The aircraft nosed over and dived into the ocean at full power. The loss of pitch control was caused by a snapped elevator cable. If the cable had snapped at a higher altitude, the pilot may have had time to use the elevator trim tab to regain partial pitch control and not crash with such severity.
Those other accidents you mention were very different. In both cases the loss of control started at high altitude and the pilots had enough time to establish partial or limited control. They were able to maintain some control up until the time of impact. The impact G forces were therefore far less and were survivable for many of the passengers.

There's a simple physics principle you need to keep in mind

Increase the distance, decrease the force

The aircraft in question cruises at about 200MPH. It nosedived into water (which probably accelerated it some). At that speed, water acts like a solid

A good way to think about high-velocity impacts is not in terms of things (like water) acting more solid, but in terms of things (like people, rocks, Fabergé eggs) acting more fluid.  The more energy that’s involved in a collision, the less important the binding energy (the energy required to pull a thing apart) is.  A general, hand-wavy rule of thumb is: if the random kinetic energy of a piece of material is greater than the binding energy, then the material will behave like a fluid.  A bit more energy, and it will fly apart.
So, when you fall from a great height and land in water there’s a bunch of kinetic energy going every which way.  The water continues to behave like water, but since the kinetic energy in different parts of your body are greater than the binding energy keeping them connected, then the body as a whole will act more like a fluid.  That is; it’ll “splash” (in the grossest sense).

In other words, the impact victims took the brunt of the impact energy themselves, thus destroying their bodies (i.e. they died). Had the pilot leveled off before hitting the water, the water would have absorbed far more of the aircraft's energy.
This is why, for instance, United 1549 had no fatalities. In this recreation (relevant portion starts about 3:00) you can see the aircraft enter the water parallel to the water and slow down.


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Does a full set of legible structural engineering drawings for the Hughes H-4 Hercules still exist?
I am not looking for unreadable images or pictures of images, but a fully legible copy or print.
I have found a reference to a set of drawings at UNLV however no contact info nor a department to contact

I would think so but no. Also I would think there would be copies in the library of congress since they investigated it but no on that as well

I would contact the Evergreen Air and Space Museum in McMinville, OR. They currently have the actual H-4 prototype and their curators may be able to help.

According to Wikipedia the aircraft division was sold to Raytheon. Maybe they have retained the original blue prints of the aircrafts...

Contact the Evergreen Aviation & Space Museum and speak with a Docent.
https://goo.gl/maps/EDfpig8RVzSj85U28

Wonder if the Hughes H-4 in Microsoft Flight Simulator was modeled based on original drawings, or just ad-hoc measurements, photos and LIDAR scans of the preserved aircraft.


text:
What is the procedure to enter, maintain and recover from a flat spin?
Looking for a play-by-play from the pilot's seat of a Pitts biplane. What thoughts, considerations and control inputs are required to enter & maintain a flat "pretty" spin and a calculated exit path?
Visual example:
What is going on in this guy's head, his hands and his feet?

The tail is way high in the video.  I don't know that I would even call that "flat".  I think it's more along the lines of Youtube click bait.

If I remember from flying the Pitts S-2B, entry into an inverted flat spin was fairly easy, starting from an entry in the vertical, similar to performing a hammerhead stall, but using a excess of rudder with insufficient aileron pressure.  Another method is the fly a Lomcovak, which inevitably terminates in an inverted flat spin.
Again, it all depends on the edge of the envelop characteristics of the aircraft in question.  And some aircraft may not be recoverable at all once a flat spin is entered.  With aircraft certified to fly this kind of an aerobatic maneuver, recovery is fairly simple with motions being countered with rudder and elevator pressure.

Could you describe the experience from the pilots seat of your Pitts?

Also, not inverted, although both are curiosities to me. I'm mainly concerned with upright flat spins

Depends on the aircraft. A flat spin is an aggravated "normal" spin with a rearward CG. Some aircraft are notorious for being difficult if not impossible to recover from flat spins. Several WWI & WWII, F4, and F111 fighters were well known for not recovering.  https://en.wikipedia.org/wiki/Spin_(aerodynamics), and http://www.robertnovell.com/blogscience-spin-recovery-february-21-2014/

I added, in a Pitts biplane

"And some aircraft may not be recoverable at all once a flat spin is entered" - I thought that (in the U.S., at least) one of the certification requirements for all aircraft was that they had to demonstrate recovery from a flat spin?

This is what works in my Pitts S1 for an upright flat spin.
From level flight with power at idle, slow to stall speed, 55-60 knots. When the nose drops apply full Left rudder (it must be that way with a right-turning Lycoming engine) and pull the stick all the way back.
We are now in a normal upright spin to the left. After about one turn, apply and hold full right aileron. This flattens the spin a fair bit. Then open the throttle, the more power, the flatter the spin. The yaw force on the propeller disc is precessed 90 degrees in the direction of rotation to become a nose up force.
With full throttle, the nose comes up to the horizon and there remains about 20 deg of left bank. The airspeed indicates zero, the rotation rate is less than a normal spin and the rate of descent is a lot less.
This spin in my aeroplane is smooth and stable, like sitting in a rotating armchair with engine noise.
Things on the horizon are whizzing past quickly when looking out and I mainly watch the altimeter.
Unlike some other spins that you can do in the Pitts this one is not heart-thumpingly exciting, it is almost relaxing. But the altimeter is unwinding….
For the recovery I follow the procedure from a textbook written by a highly experienced aerobatic competitor, instructor and judge.
Leaving the power on, apply full Right (anti-spin) rudder and hold it there. Then make sure you start with the stick in the right rear corner. Then while holding full back stick apply full left aileron. Then holding full left aileron start moving the stick forward. You make an ‘L’ shape. The S1 stops rotating very quickly after that, the nose goes down at the same time and you are flying again. Centralise controls and recover from the dive.
The same technique works with power off but it will take longer. This was Eric Muller’s method.
The Beggs-Muller Power Off, Hands Off, Opposite Rudder ‘Emergency Spin Recovery’ technique also works in the Pitts, but the above power on method is the quickest.

There are other possible entries.


text:
How can I learn air traffic control as a high-schooler?
I really love aviation and I'm thinking about going for a career in air traffic control, but I can't find anything on the web that will help me learn all about it and how to perform basic operations. Is there anything on the web that I could use?

@Dave this didnt help me much though.

this will most likely get closed as the other answer does cover the question pretty explicitly. I have un-deleted an answer here I was working on before I noticed the dupe. It has some more info in it as well.

Call your local control tower and ask to take a tour.

Join the Vatsim network.  This is a network of simulated pilots flying X-Plane, FSX, etc., and simulated controllers.  The simulated controllers use, as much as they can in a hobbyist network, real phraseology and procedures.  I personally knew several real-world controllers who controlled on the Vatsim network in their off-time, and I know several hobbyist controllers who went on to become real air traffic controllers.
While controlling on a hobby network is not the same as controlling real airplanes, you won't learn a lot you'll have to relearn.  That's because the hobbyist controllers on Vatsim make a serious effort to follow real procedures.  When they discuss air traffic control with each other, you frequently see references to the ".65", the official bible of ATC.

The FAA lists a lot of the ATC info here. They also offer a really nice "example" flight worth of communication for those interested in what its like.
You can stream the US ATC feeds from most major airports from this site. A good resource once you have some context on what they are saying.
The airplane instrument flying handbook is intended for pilots but has lots of IFR flying examples and information with ATC communications as well.
My local airport offers (or at least offered at one point) tours of the tower. You can usually set one up by calling the phone number for the field. This is a neat way to see at least part of the working environment and possibly meet a controller and ask them questions.


text:
What is the actual range of ICON A5?
Does anyone currently own or have experience flying an ICON A5 aircraft?
They claim a range of 300 NM (555.6 km). I would like to know whether this is a theoretical calculated range, or a true/actual number?

I didn't realize they'd started delivery yet... How many are in customers' hands?

@egid to my knowledge, only a handful, but they started shipping late 2012.

They haven't started production for customers yet, according to a press release on their website: http://www.iconaircraft.com/production-update-2-october-2013.html. This does mean that we have no other source for the actual range of the ICON A5, except if we could find some test flight article that actually flew the aircraft long-distance.

Hm, it appears you're correct. Shame! I can't find where I read about 2012, etc.

As of 2020-07, the Icon A5 Specifications page says Range: 427nm (45 min reserve).

I can't speak directly to the ICON A5 as I neither own nor fly one, but for every aircraft I'm familiar with the manufacturer's "book numbers" are generous theoretical values - for example, they typically assume flying perfectly straight-and-level in a no-wind condition, and getting the best possible fuel economy performance from the powerplant.
The Icon folks are openly honest about this on their specs page: Performance specifications are estimates only., and range is certainly "Performance" in my book.

Personally I have no doubt that the A5 could manage 300NM under the conditions for which its designers did the math to arrive at that number - it's a slick little plane with a fuel-sipping engine - but they may have done a "to empty tanks" calculation (leaving you to account for the VFR fuel reserves you're legally required to have), and in the real world the 15-knot headwind you run into will substantially reduce your range (or, conversely, you can fly in the other direction and increase it).
As with all aircraft your mileage will, quite literally, vary depending on the day and direction of flight.

Sounds reasonable - thanks for the answer ;) thankfully the A5 comes with the emergency parachute :P

It's worth noting that useful load is only 430-450lbs. A full tank and oil gives you < 310lbs. for you and a friend.

@Levesque Hey, we're all FAA standard 170lb adults here right?

I don't have experience with this aircraft, but their website lists the range as "427nm (45 min reserve)".
https://www.iconaircraft.com/a5/

Due to a wide range of cruise altitudes, cruise engine power settings, atmospheric conditions and winds aloft, range and endurance vary considerably.
But the Icon A5 Pilot Manual, Section 5.11 - Range and Endurance (pp 84-85) indicates a maximum endurance of 6.7 hours at 4500 RPM and a maximum range of 473 NM at 5000 RPM.  The data is only applicable at 10,000 feet pressure altitude and STD + 20°F temperatures, zero wind, full fuel at startup and in the configuration specified. The data also includes a fuel consumed during startup, takeoff and climb to altitude and also includes a 45 minute fuel reserve at 10000 ft @ 4500 RPM.

The promotional video of Icon shows it flying from Miami to the Bahamas, which is 600 km round trip. So it probably can.

This mentions no refueling, no numbers at all.  For all we know, the airplane was towed there and back.  For all we know, the airplanes at either end were different ones.


text:
Where does the FAA state requirements for how long grass can be?
Working on a maintenance program for my local southwest airport, can you tell me what FAA document specifically states that the FAA recommends grass or turf height to be 5 to 8 inches?

"Turff"? - Turf?

Possible dupe, although that question doesn't say which country or regulator it's asking about and there's no useful answer (yet).

Have a look at this Advisory Circular. There are numerous recommendations involving vegetation, but I couldn't find specific heights for grass mentioned. It DOES recommend lower growing turf, and discing or plowing taller grasses (milo, ryegrass) before they can seed out.
https://www.faa.gov/airports/resources/advisory_circulars/index.cfm/go/document.current/documentNumber/150_5200-33


text:
Are empennage airfoils always symmetric in conventional airliners?
I'm specifically interested in these models: A319, B737-700, A220, E195-E2. You could call these conventional airliners, so I suppose the question is if these "conventional" planes have only symmetric airfoils in their horizontal and vertical stabilizers. Also, these empennages would never have supercritical airfoils?

The CRJs have negative camber on the horizontal tail and I believe a lot of airliners do, since they are generally making negative lift for trim.  The vertical is always symmetrical.  The horizontal tail of the RJ is definitely not supercritical, although the main wing is.

Interesting chapter on empennage design (Raymer).


text:
Can a 16 year old student pilot "pre-take" the checkride?
I am a student pilot, and I soloed about one month after my 16th birthday. I know I can't become a private pilot until I am 17, but I'm wondering if there is a way to take the check ride before you are 17, but be limited to the privileges of a student pilot until you are 17, at which point you can exercise the privileges of a private pilot? I doubt it, but its worth asking. I feel like I am pretty much ready to take the check ride, but I have to wait 8 more months. Thanks!

14 CFR Part 61.39 (a)(5) states that you can not take a checkride in the US until you are of age to hold the desired certificate.

(5) Meet the prescribed age requirement of this part for the issuance of the certificate or rating sought;

Sorry. I encourage you to take as many mock-checkrides as possible in the meantime.
Also, in addition to mock-checkrides. You can train for your instrument rating. 14 CFR Part 61.65 allows you to take a combined checkride or even back-to-back private and instrument checkrides.
§61.65 Instrument rating requirements.
(a) General. A person who applies for an instrument rating must:
(1) Hold at least a current private pilot certificate, or be concurrently applying for a private pilot certificate, with an airplane, helicopter, or powered-lift rating appropriate to the instrument rating sought;

thank you so much for your response @DeanF. That is really helpful, I never considered the possibility of combining private and instrument training. How would that work, because don't you need a minimum of 50 hours of cross-country flight as a private pilot in addition to the required instrument training in order to take the instrument check ride?

@GeckoFox1001 - 14 CFR Part 61.65 (g) goes on to say
(g) An applicant for a combined private pilot certificate with an instrument rating may satisfy the cross-country flight time requirements of this section by crediting:
(1) For an instrument-airplane rating or an instrument-powered-lift rating, up to 45 hours of cross-country flight time performing the duties of pilot in command with an authorized instructor; or

So just to make sure I understand, 45 of the required 50 hours of cross country pic time can be fulfilled by dual training that is not cross country? Since I already have around 45 hours of dual training and 5 hours of solo cross country, does that mean all I have to do is take the instrument written and do 40 hours of instrument training to take the combined checkride?

@GeckoFox1001 No, those 45 hours have to be dual xc. And talk with someone who has done a combined check ride before you consider going down that road.

@GeckoFox1001 - 61,65(g) only allows you to substitute an hour of dual cross country flight time performing the duties of PIC while not a certificated pilot for each hour of cross-country PIC flight time when certificate up to 45 hours.


text:
Should a student pilot use their license to go somewhere?
I’m a student pilot, and I want to meet my friend for a couple of hours at an airport away from my home airport. I have all my minimums done, but I’m just waiting to take the check ride. I’m wondering if it is ok for a student pilot to use their license for something other than a training flight and actually go somewhere for a purpose? (obviously, I’ll have all my endorsements).

What country are you referring to?

As a CFI I would be hesitant to sign off on this.  Too much gettheritis risk and a lot of pressure for the student to "make it work" to impress a friend/keep to a schedule.  I don't think there is a legal problem, however.  It's essentially just a solo flight to have lunch somewhere.

This is "primarily opinion based". There is no definitive answer, nor any way to glean one, and so is not appropriate for a Stack Exchange site.

Entirely disagree with "opinion based." Either this is a legal plan, or it isn't. That's perfectly clear-cut, no opinions involved. If we want to speculate about what weather or airports or attitudes or whatever else might influence a CFI's willingness to sign off on the XC, then those questions could bring "opinion" factors into the picture, but that isn't what I see being asked. At all. VTLO.

Based on your previous questions, I added the faa-regulations tag because it seems very likely that you're asking about the US. If I got that wrong then of course you can simply remove it. Please always tell us which country you're asking about for questions on regulations, standard practices etc. because things can be very different in different parts of the world.

Is this a question about "should" (and that is an opinion) or about "legally could" (and that's not an opinion) ?

@RalphJ the question is in that case too broad as it does not limit itself to the legalities. By asking "is it ok" it sets itself up to be opinion based from the get-go.

Thank you guys for the responses. First of all, yes, I am talking about the US. I should have specified that. Secondly, my question is more opinion based. I’m fairly positive there is no regulation against it.

Downvoting as this is opinion-based.

@KennSebesta add a VtC - more useful that way

I'm going to answer this from the purely regulatory point of view as asking is you should do something is subjective and therefore off-topic as opinion based.
There's no regulation in any jurisdiction I know of that would prevent you from doing this, cross country flying is part of getting your ticket and nothing says you can't do something while you land away. It's not something typically done on a qualifying cross country, the point is to get it done in the time frame allotted and get back safely.
Once you have your qualifying flights done other cross country flying is at the discretion of your instructor, who would make a decision based on a number of factors like your readiness, distance and complexity of the flight, potential hazards and his/her own workload - remember that instructors are responsible for you while you are on that flight so they have to keep tabs on you, which takes work. By all means have the conversation.


text:
Which class B airports support GA?
As a student pilot (soon to be private pilot), flying into any class B airport is intimidating. Many class B airports simply do not support general aviation and discourage pilots from coming in. For example, I know that the fees for landing at JFK are insane, and it would just not be practical or feasible to pick someone up who arrived on a commercial flight. My question is: are there any class B airports that support GA operations, and are there any at which it would be reasonable to fly in and pickup someone who arrived on a commercial flight?

Off the top of my head, PIT has seen a major decline in traffic since the USAir/American merger, to the extent that the Class B airspace is probably not really justified any longer. I've seen comments on reddit saying it's relatively easy to get into in GA aircraft.

I know many private pilots (even before the pandemic) that flew into ORD. Every Class B with an FBO should be fine for GA operations, but you really have to be on the ball. VFR may be denied all together (call ahead to work it out with the tower, don't just show up), but if you are IFR and have filed a plan, they have to work you in.

Aside from NY and DC, pretty much all B airports are GA-friendly as long as you have good radio skills.

KBWI (Baltimore) is fairly GA-friendly. There’s a small flight school on the field, Signature has an FBO, and GA parking is available. SR22s fly in and out all the time, and other larger GA aircraft are VERY common (I live under the approach to 15R and have a clear view of aircraft approaching 15L. BWI’s RWY 15L/33R is used exclusively by smaller aircraft- small/mid bizjets, GA, and a few small airlines operating PC-12s and C208s. I’ve seen more than once 172/152s doing touch and goes here.

Some private pilots make a point of flying into Class B airports whenever they can, just to get the experience. A few of these are on YouTube, such as Martin Pauly, who flew into JFK, stayed overnight and departed VFR in his Bonanza. You may find such videos interesting (but as always they are not intended as flight instruction).

Many of the busier airports will levy obscene landing fees or the FBO's will charge very high ramp fees. A few years ago I flew into SFO in a Citation II. Between the landing fee and ramp fee I think my cost was in excess of $1,000. So lander beware: The fees can be quite high and not necessary uniformly disclosed.

Short answer; Basically all of them, but for the 7 landing slot airports you might need to pre-arrange your arrival.
It really depends what is going on at the airport, how willing you are to pay the fees, and if you feel confident handling the radio chatter as well as some possibly complicated taxi instructions. Pretty much all airports support some kind of private jet traffic so there is no reason you cant fly a dinky little PA-28 in. However if you intend on even considering this, keep in mind that you might get vectored elsewhere or not cleared for landing and if you do get in; expectations will be HIGH. In my experience controllers will not be happy about slow read backs, improper phraseology, taxi errors, or general confusion, there is a very good chance there is an airliner behind you and they are not going to be happy if they need to go around because you didn't vacate the runway expeditiously.
Ive landed at KPIT in a PA-32 that I was flying for a business trip, like any Class C airport of comparable size they had a pretty nice FBO that was not cheap... Its really no different than landing anywhere else with the exception of our approach being somewhat faster than usual as we were sandwiched between two airliners inbound.
During the pandemic I was even able to fly into JFK/EWR/LGA in a buddies C-172 all in the same day. EWR even sent us our own marshaling van which was bigger than the 172... While this was a somewhat special case as there was effectively no commercial traffic it is still very possible to land there in a GA aircraft.
KPHL supports GA operations and I'm pretty sure few light singles are even based there. It looks like KSFO has an FBO that supports private aviation and according to foreflight it looks like they do sell 100LL so they must expect something with a piston engine to show up. JFK also has a nice FBO you could use and here is a good account of a Mooney flying in. You can check up on the other major airports for similar facilities.

Its worth noting (since you are a student pilot). Its not all that uncommon to over-fly class B airports (at least its not in the PHL area I have done a lot of my flying) and even though these airports can be hard to get into normally in an emergency they will be more than happy to help out.

Most* class B airports are surprisingly GA friendly if you are prepared. Martin Pauly has many YouTube videos of flying into class B airports all over the country in his Bonanza.
However, there are several challenges your primary training probably didn’t cover or prepare you for.
Radio skills
As a student, you aren’t even allowed into class B airspace (without an extra endorsement) because it’s assumed you won’t have good enough radio skills, and ATC is too busy to hold a student’s hand like they will at class C or D airports. Even many private pilots don’t acquire decent radio skills until they go through instrument training. There is no substitute for practice, so discuss with your CFI.
Traffic volume
Many class B airports are among the busiest in the world. However, that is mostly during the day, and they can seem like ghost towns at night. And even during the day, there will be “pushes” when a lot of planes arrive or depart and lulls between those pushes. If you call ahead, they can tell you the best times to arrive/depart; if you show up at the wrong time, especially VFR, you may end up holding for an hour or more until things calm down enough for ATC to deal with you.
A controller at SFO years ago told me about a Cherokee that showed up in the middle of a push asking for a touch-and-go. Rather annoyed and just wanting to get rid of him, they told him to “come back at 3am.” He indeed came back at 3am, and they were so amazed (and bored) that they actually let him do pattern work!  Timing is everything.
Traffic speed
As a new private pilot, you’re likely flying slow piston planes that normally land at half the speed a jet does. This makes it very hard for ATC to fit you into the flow of traffic. Ask your CFI to show you how to do fast, no-flap landings, which will reduce (but not eliminate) the speed disparity and make things easier for ATC. Flying final at 100kt+ in a C172 or PA28 is not easy, but it can be done. Also ask about short approaches, which are another way you can help ATC fit you in, and long landings to avoid jets’ wake turbulence.
Taxiing
The taxi instructions you get are probably going to be longer and more complicated than any you’ve ever heard before. Some airports even have named routes (see the A/FD). Study the taxiway diagrams ahead of time so you’ll have a good idea what to expect, and that’s half the battle when it comes to radio skills.  Also, since you’ll be calling ahead anyway to find the best time to show up, ask what runway to expect as well. Some B airports actually have a designated GA runway, and those that don’t will fairly predictably put you on the runway furthest from the airline terminals.
Worst case, you can ask for progressive taxi, but be prepared enough that you shouldn’t need it.
Fees, fuel and FBOs
Every B airport will have at least one FBO, and they pay huge rent to the airport, which gets passed on to you in the form of ramp fees. They will often waive or at least reduce those fees if you buy their overpriced gas, which you may need anyway. Call ahead and ask. Note that while the fees (or fuel) may be pricey, it may still be cheaper than landing at another airport and having your passenger take a taxi between the two.
Also, you’re not the first pilot doing what you propose; FBOs often shuttle passengers to/from the airline terminals. But they may need to know ahead of time to make sure a driver will be available, so mention that (or any other services you’ll need) during your call. They may also have security rules you and your passengers will need to follow, so ask about those as well. Be aware you are responsible for your passengers’ safety once they step out onto the ramp, so if they haven’t flown GA much, keep a very close eye on them.
Weather
Keep in mind the airlines will keep flying in conditions that you can’t, so always have a backup plan in place if you are unable to pick up your passenger—or get them back in time for their flight. Pressure to be there on time is a good way to put yourself into a situation you aren’t prepared for, which tends to be a fatal mistake. Your only goal as a student or private pilot is to arrive alive; let the professionals worry about schedules.
On the plus side, if the weather is even moderately bad, ATC won’t let you anywhere near a B airport anyway, and knowing that should help you avoid even attempting it.
Most, not all
There are a few airports that you shouldn’t even bother thinking about: JFK, LGA and DCA. These airports are slammed nearly 24x7 with airline traffic, and even IFR jets can’t get in without a slot reservation. And DCA also has security restrictions due to the SFRA/FRZ. You might have had a shot last year during the COVID downturn (as @Dave comments in his answer), but hopefully another event like that won’t happen again in our lifetimes.

If the traffic is light, even weather may not be a problem. I once went up with my flight instructor at night, I think about 10:30 pm local time, for some instrument work. We asked for a practice ILS approach at KMSP and it was approved! Flew the approach in actual IMC until they called our missed, which was a bit above minimums. Got a look and could have landed easily enough. It never hurts to ask.

@FredLarson Once he has his IR, sure, but that changes a lot of other things too.

KCVG i know is very friendly to GA aircraft. I don't think i've ever heard them Deny a request and they will let you fo touch and goes / stop and goes during the day but during the night they are more restrictive on what GA aircraft can do cause of all the cargo flights coming in

CVG handles a fraction of the traffic that other Bravos see- 1/3rd the operations and 1/6th the passenger count as SEA, even less compared to LAS or JFK. It’s fairly high on cargo though.


text:
What is the typical wing twist angle at the wing tip for a commercial jet?
I'm trying to find this information for commercial jets. It is nowhere to be found. Does anyone know typical values?

Do you mean the built in wing twist to adjust for lift distribution across the wing, or the induced twist that can occur when making use of your ailerons?

@Noddle Built in wing twist.

This is usually called wing washout or washin (depending on which way it twists), which may help your search

For an A310 we start from the attack of the engines with an angle of attack of the profile of 3 degrees, and we arrive at the wing tip to -3 degrees. In general along the wing the twist angle is around 2-3 degrees, it is near the tip that changes and arrive until a negative value.

Commercial jets are special because they change airfoil shape over span quite dramatically to reduce the effects of sweep on local lift. Also, the lift force on a backward swept wing causes it to twist, so washout in flight is several degrees higher than on the ground.
In order to compensate for the much higher zero-lift angle of attack of the modified root airfoil, its incidence is very high. If you use the fuselage axis as a reference, in case of the A330 and A340 the incidence changes from +4.5° at the root to 0° between 30% and 70% span and -2° at the tip when on the ground and -2° at 70% span and -5° at the tip in flight.


text:
What is the absolute ceiling of the A319-100, B737-700 and A220?
What is the absolute ceiling of the A319-100, B737-700 and A220? I have found the service ceiling in Jane's and their type certificate data sheets, but nothing on the absolute ceiling.

The absolute ceiling is a very dangerous place to be.

For a sufficiently light aircraft (since max altitude varies with weight & atmospheric conditions), it would be well above the max certified altitude. Which means you'd need test flight data -- nobody's going to publish stuff that assumes/encourages flying above the operating limitation of the max certified altitude.

@JohnK, why is an absolute ceiling a dangerous place? You just set full power, maintain Vy with pitch and keep climbing until it won't climb any more. Now coffin corner (which is what these aircraft are limited by in practice) is of course a different matter.

Because you are balanced on a knife edge in terms of energy state and if anything goes wrong, like a bit of inattention or distraction that causes that last bit of surplus energy to be consumed, your only choice is to dive, hard.  Even at service ceiling, you have to carefully monitor airspeed.  A little bit of smooth down-side mountain wave that starts you descending 100fpm will be corrected by the A/P with a pitch up, which will bleed off speed, and if you are already close to min drag and distracted for enough time, before you know it the shaker is going and the only option is to dive.

From prof. Wittenberg's half-a-century-old lecture book, paper copy only, translation and interpretation fully on my account. Way before any A320 family aeroplane...

The pic is relevant for propeller aeroplanes, and indicates a theoretical ceiling (max climb speed = 0) that is about 5% higher than the service ceiling (max climb speed = 100 ft/min). The theoretical ceiling will only be reached after an infinite amount of time, since the climb speed is ever decreasing.

For high subsonic aeroplanes like the B737 and A320 families, there are additional limitations to the max climb speed: $C_{L,max}$ as function of the Mach number is limited by the buffeting boundary. The figure above is referenced in the book as being from a high subsonic aeroplane, which may well be the Fokker 28. Resulting in altitude and M limitations as depicted below.

Note that

the figure references a turbo engine, not a modern high bypass engine;
indeed the absolute ceiling can be a tricky point to be at, diving out of it may be limited by the max. buffeting speed.

So, what is the theoretical ceiling of the A320/B737/A220? A couple of percent higher than the service ceiling, unless limited by the max. buffet speed. And it takes forever to get there.

Absolute ceiling is not a fixed number and may change from flight to flight, and even within the same flight. It depends on conditions at altitude, loading of the aircraft, etc. A lightly loaded aircraft may be able to push the envelope higher than one that is heavily loaded. That is why the number that is published is the service ceiling, which is determined after reviewing flight test results and coming up with a number that incorporates a safety margin for safe aircraft operation.